The present invention relates generally to instrumentation used for driving screws during surgery, more specifically, the present invention is suitable for medical applications involving orthopedic implants.
One of the present inventors has previously filed Swiss application no. 0839/99 on May 5, 1999, the disclosure of which is reproduced here in relevant part and incorporated herein by reference thereto. In this application there is disclosed an annular metallic ring that is perpendicularly slit, to exert a holding force against the internal wall of the socket head of a screw. However, the ring had a tendency for the free ends of the open slit to become skewed relative to one another during use. Moreover, the straight tip of the driver did not always exert uniform contact with the mating female socket wall to transfer torque without significant rotational play within the socket. This is disadvantageous to surgeons who require an instrument that gives them a precise feel for where they are placing the screw. Instruments of this type are typically manually driven either by a handle grasped by the surgeon, or, they can be connected to a powered hand tool. The screw must be securely held while pre-assembled with the male end of the tool during inter-operative insertion. The surgeon must have precise control without risking that the screw will separate from the tool and fall out, e.g., while manipulating it before it is driven into the bone.
It is known to use a driver with tapered tip that seeks to wedge into the socket head of a driven screw; however, this approach did not use retaining rings to hold the driver and screw together during placement. As a result, if the tolerances weren't just right the weight of the screw would overcome the wedging force keeping the driver tip in the socket, so the screw tended to fall unpredictably off the tip during surgery.
Another prior design of the present inventor employs the C-shaped ring, mentioned above, to temporarily hold the cutting tip of a modular flexible reaming system onto the shaft. This allows the assembly to be passed from a nurse to the surgeon without the components falling apart onto the non-sterile floor. It also allows the nurse to change the tip from one size to another rapidly, as the surgeon progressively reams a bone canal. It is contemplated that a C-shaped ring can be useful as a pre-tensioning member in such a temporary male-female assembly. However, the present inventor has generally observed that this problem occurs whenever a C-shaped ring is used to hold a male and female member together temporarily. The ring can still catch on the entrance to the female socket, causing the connection to malfunction. Conversely, if the ring is mounted inside the female socket, i.e., instead of on the male tip, the present inventor believes that similar problems would result.
Accordingly, there is a need for a tool with a retaining ring that temporarily holds together a driving member and a driven member, e.g., a driven screw, where the ring has no exposed edges that might cock the tip in the socket and thus impair operation. Similarly, this need extends to other surgical applications, such as temporary retention of a reamer cutting tip with a shaft.
There is a further need for providing a driving tool that has improved wedging contact between the tip and socket head to give a solid feel to the surgeon's hand during an operation, while securely holding the screw and tip together during surgical placement.